Semiconductors are continually being fabricated on smaller scales as technology moves forward. Measurement techniques must similarly evolve so that tighter device specifications can be properly monitored and maintained. Currently, samples are often measured utilizing metrology techniques, such as ellipsometry, reflectometry, and the like. Scatterometry models may be utilized to fit data collected from a measurement target of the sample to determine sample parameters at higher degrees of precision and accuracy.
Three dimensional memory stacks and other multiple layer samples may have repeating structures with high correlation between parameters characterizing multiple layers, deep contact holes, and other challenging structural attributes. The complex sample structures tend to make it difficult to determine sample parameters with a high degree of accuracy and precision. Multiple tool or multiple target measurement techniques may be employed to improve sensitivity to complex sample parameters. However, data collected from multiple tools or multiple targets continues to be limited by structural uncertainties.